This invention relates to vehicle light sensor systems, and particularly to a light sensor for an automatic headlamp dimmer.
Improved automotive control systems have freed drivers from performing a number of tasks that formerly required manual operations. Such systems relieve drivers from the distractions of these auxiliary systems and often can result in improved concentration and reduced driver fatigue. Key to the operation of such control systems is a means for sensing a condition to which the control system must respond. In automatic cruise control systems, for example, the sensed condition is the vehicle's velocity. In a number of systems, such as automatic day/night mirror controls and automatic headlamp dimmers, the condition to be sensed is the presence or absence of lights from other vehicles. For example, in automatic headlamp dimmer systems, when the headlamps are on, the control system normally sets the headlamps to the high beam mode unless the system senses the presence of another vehicle's headlights or taillights immediately in front of the subject vehicle.
While numerous automatic headlamp dimmer control systems have been developed, in general, many of these systems have had serious drawbacks due to their performance, complexity or cost. One area of difficulty has been in their packaging and optics. Since these systems must sense light from headlamps or taillamps from other vehicles, a key requirement is that the system be able to distinguish this light from extraneous incoming light. Examples of such unwanted light includes reflections from road signs, light from street lamps, or light from vehicles on other roadways. To overcome this problem, some prior systems have utilized various kinds of optical chambers surrounding a light sensitive detector to prevent unwanted light from reaching the detector. However these chambers are often bulky, expensive, and prone to permitting light to leak into the chamber. In addition, off-axis light rays from outside the desired entrance angle are sometimes scattered within the chamber until they reach the detector. This will degrade system performance and may necessitate a lower detector sensitivity.
In other prior headlamp dimmer control systems, separate aperture plates are utilized to define the desired entrance angle for the detector. However, in general, due to the distance between the aperture plate and the detector, a somewhat diffuse angular cutoff results. This yields less precise control over the entrance angle of light into the detector. In addition, with such aperture plates, misalignment or damage during manufacturing, shipment, or use, is likely to occur.
Another difficulty with prior automatic headlamp dimmer systems results from the critical alignment requirements of the optical components of the systems. In particular, in many systems, the distance and orientation of the detector, aperture, and lens must be held to within small tolerances. During mass production, changes in these tolerances (for example due to mold shrinkage) can necessitate separate operations to fine-tune the position of the lens or detector after manufacturing. This often requires expensive and time consuming machining operations.
In addition, prior automatic headlamp dimmer sensors do not generally take into account the varying intensity of the light to be sensed over the field of view. Since oncoming headlights to the left of the vehicle are much brighter than the taillights immediately in front of a vehicle, the detector must be sensitive over an extremely wide range of light intensity. This makes the system more susceptible to noise or to unwanted scattered light.
Accordingly, there is a need for a vehicle light sensor which is compact, inexpensive and easy to manufacture. There is also a need for a vehicle light sensor which precisely controls the entrance angle of the light and is not affected by light outside this angle. It is further desirable to provide a vehicle light sensor which is stable in manufacture and holds the optical components in precise alignment. It is also desirable to provide such a sensor which takes into account the varying intensity of light over different parts of its field of view to minimize the required range of sensitivity of the sensor.
In accordance with the present invention, a vehicle light sensor having the above-described desirable features is provided. The light sensor includes a detector for producing an electrical signal in response to incoming light. The detector is housed in upper and lower enclosure members. A lens receives light and focuses it on the detector. One of the enclosure members has a receptacle for mounting the lens. The upper and lower enclosure members also form an optical chamber adjacent to the light detector to prevent light that does not pass through the lens from reaching the detector. In addition, a plurality of optical baffles are provided within the optical chamber for preventing light from outside a desired entrance angle from reaching the detector.
In accordance with another embodiment of the present invention, the vehicle light sensor includes a thin aperture plate attached to the detector. The plate is opaque to light for preventing light from reaching the detector. An opening in the aperture plate permits light to reach the detector in selected areas. This opening may be in any predetermined shape to obstruct light in certain areas of the field of view of the detector and may also include shaded portions to reduce the intensity in selected portions of the field of view. Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims taken and conjunction with the accompany drawings.